Semiconductor Device and Power Supply Unit Utilizing the Same

ABSTRACT

A semiconductor device has pluralities of grid array terminals forming a grid array structure, e.g. a BGA structure, in which the output end of a built-in switch circuit is connected to multiple terminals of the grid array structure, thereby reducing the current that flows through each of the multiple terminals below a permissible level and minimizing the heat due to contact resistances of the multiple terminals in contact, with the IC socket of the semiconductor device. Each pair of nearest neighbors, of the multiple terminals is interposed by at least one further array terminal. The multiple terminals are all located at the outermost peripheral terminal positions of the grid array structure. Thus, the heat generated in the respective multiple terminals connected to the switch circuit is reduced, thereby minimizing the possibility of hazardous melting of the terminals.

FIELD OF THE INVENTION

This invention relates to a semiconductor device having built-inswitching transistors, and a power supply unit utilizing suchsemiconductor device.

BACKGROUND OF THE INVENTION

There have been widely used switching power supply units having anintegrated semiconductor circuit that includes a switching element (e.g.transistor switch) and a drive circuit controlling the switching elementto control the output voltage of the switching power supply unit.

FIG. 3 shows a circuit arrangement of a conventional switching powersupply unit, in which a semiconductor integrated circuit (IC) 10 has atransistor switch Qo and a drive circuit 20 for driving the transistorswitch Qo. This transistor switch Qo is directly connected in series toa coil Lo via a pad Po of the IC 10. The voltage appearing at the nodeof the pad Po and the coil Lo is rectified and smoothed by a diode Doand a capacitor Co to provide a dc output voltage Vout.

As the transistor switch Qo is turned on, switching current Io issupplied from a power supply (e.g. a battery) having an input voltageVin to the transistor switch Qo via the coil Lo and the pad Po, and thetransistor switch Qo. The current Io grows larger with time after thetransistor switch Qo is turned on. If the transistor switch Qo is turnedoff, the energy accumulated in the coil Lo is liberated therefrom, whichis rectified and smoothed by the diode Do and the capacitor Co before itis provided as the output voltage Vout of the power supply unit,converted from the input voltage Vin.

The magnitude of the output voltage Vout is determined by the duty ratioTon/(Ton+Toff) of ON time Ton to OFF time Toff of the transistor switchQo. Usually, the duty ratio is controlled by feeding the drive circuit20 a feedback voltage indicative of the output voltage Vout in such away that the feedback voltage equilibrate with a predetermined referencevoltage, thereby holding the output voltage Vout at a predeterminedlevel.

There is a combined resistance Rp for the pad and the bonding wireconnected thereto that arises from the resistances of the pad Po and thebonding wires and the contact resistance therebetween. In FIG. 3, thecombined resistance Rp is shown in parentheses. A voltage drop caused bythe combined resistance Rp will result in an electric power lossdetermined by Rp and Io.

In order to reduce the voltage drop due to the combined resistance Rp,multiple bonding wires can be parallelly connected to the terminal (see,for example, Japanese Patent Applications Laid Open No. H7-202097 andNo. 2000-114307).

A wafer-level chip-sized package (WL-CSP) type IC has been increasinglyadopted for miniaturization of the IC. A WL-CSP type IC has pluralitiesof ball-shaped terminals (hereinafter referred to as ball terminals)arranged in a two-dimensional grid array structure (the terminals in thestructure referred to as ball grid array (BGA) terminals) to establishelectric connections with external circuits. Each of the ball terminalsis made very small in order to attain a high terminal density in the ICpackage.

It is therefore difficult to connect a multiplicity of bonding wires inparallel to a ball terminal of the BGA structure as shown in the abovecited references. Moreover, since the ball terminals are arranged in thelattice structure, it is also difficult to make a particular terminal,such as one connected to a transistor switch, larger than otherterminals.

It is noted that the current Io has a comparatively large magnitudesince it pertains to the switching of a transistor switch, so that itcan exceed the withstand current level (or permissible current level) ofone ball terminal. The ball terminal connected to a semiconductor switchgenerates heat determined by the contact resistance thereof and thecurrent Io. As a consequence, these ball terminals connected to atransistor switch are in jeopardy of being melt down by heat.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide asemiconductor device equipped with a built-in switch circuit and a drivecircuit therefor and having pluralities of grid array terminals forminga grid array structure such as a BGA structure, wherein the multipleterminals to which the switch circuit is connected are adapted togenerate only a small amount of heat, thereby decreasing the possibilityof hazardous melting of the terminals.

It is another object of the invention to provide a power supply unithaving improved conversion efficiency, utilizing such semiconductordevice as stated above.

In accordance with one aspect of the invention, there is provided asemiconductor device equipped with a switch circuit and a drive circuitfor performing ON-OFF control of the switch circuit and having gridarray terminals forming a grid array structure, wherein the output endof the switch circuit is connected to multiple terminals of the gridarray structure. These multiple terminals may be called as switchingoutput terminals.

Each pair of nearest neighbors of the multiple terminals may be providedtherebetween with at least one interposing terminal other than themultiple terminals.

No or only a small amount of current flows through said at least oneinterposing terminal as compared with the current that flows through theswitch circuit.

The multiple terminals may be all located at the outermost peripheralterminal positions of the grid array structure.

The switch circuit may consist of a multiplicity of transistor switchesconnected in parallel with one another so as to be simultaneously turnedon and off.

Each of the grid array terminals may be a ball-shaped terminal.

In accordance with another aspect of the invention, there is provided apower supply unit equipped with a semiconductor device that includes aswitch circuit and a drive circuit for performing ON-OFF control of theswitch circuit and has grid array terminals forming a grid arraystructure, wherein

the output end. of the switch circuit is connected to multiple terminalsof the grid array structure;

the multiple terminals are connected with one another outside thesemiconductor device; and

the power supply unit is adapted to convert its input voltage into anoutput voltage under the ON-OFF control of the switch circuit.

In an inventive semiconductor device having a built-in switch circuitand a grid array terminal structure such as a BGA structure, the outputend of the switch circuit is connected to multiple terminals of the gridarray structure. In this arrangement, current that flows through any onegrid array terminal is reduced to or less than a permissible level, sothat Joule heat due to the contact resistance between the terminal andan IC socket is reduced, thereby suppressing hazardous melting of thegrid array terminal.

Moreover, since the switching current is shunted to multiple terminals,the power loss that takes place in each terminal and its surrounding isreduced accordingly, which provides an improved conversion efficiency tothe power supply unit.

Since each pair of nearest neighbors of the multiple terminals isprovided with at least one interposing terminal through which no orlittle current flows, a distributed heat dissipative area is providedfor the terminals. Thus, Joule heat is easily dissipated, andtemperature rise in these terminals is suppressed. Since all themultiple terminals are located at the outermost peripheral terminalpositions of the grid array structure, thicker, and hence lessresistive, external wires, can be connected to the multiple terminals,which facilitates enhanced heat radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a circuit arrangement of an IC in accordance with oneembodiment of the invention and an inventive power supply unit utilizingthe IC.

FIG. 2 shows a BGA structure of terminals on one side of the IC of FIG.1.

FIG. 3 shows a circuit arrangement of a conventional switching powersupply unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An inventive semiconductor device and a power supply unit utilizing thesame will now be described by way of example with reference to theaccompanying drawings.

Referring to FIG. 1, there is shown schematically an IC 10A inaccordance with one embodiment of the invention and a power supply unitutilizing the IC 10A. The IC 10A includes an IC chip 11A. FIG. 2 shows aball grid array (BGA) structure in which pluralities of ball terminalsare arranged in a lattice configuration on one side of the IC 10A.

Symbols Lo, Do, Co, Vin, and Vout of FIG. 3 respectively refer to acoil, a diode, a capacitor, an input voltage, and an output voltage, asin FIG. 1.

The IC 10A is a WL-CSP type IC having a reduced size. The IC 10A is aWL-CSP type IC having a reduced size. Formed on one side (e.g. backside)of the IC 10A is a BGA structure of ball terminals B1-1-Bn-m arrayed inm rows and n columns, as shown in FIG. 2.

Referring back to FIG. 1, there are shown a switch circuit consisting oftransistor switches Q1-Q3, and a drive circuit 20 for driving thesetransistor switches Q1-Q3, all formed in the IC 10A. Although thetransistor switches Q1-Q3 of the example shown herein are NPN bipolartransistors, they can be of another type of transistors such as MOSFETsfor example. These transistor switches Q1-Q3 are simultaneously switchedon and off by an ON-OFF drive signal issued from the drive circuit 20.

The switch circuit is shown having three transistor switches Q1-Q3, butit may have only one transistor switch. However, from the point ofpreventing the switch circuit from being influenced by breaking of wiresand/or loose connection of terminals, it is preferred to provide theswitch circuit with at least two transistor switches. Furthermore, ifthe switch circuit has more than one transistor switch, it has extracurrent drive capability.

The collectors of the transistor switches Q1-Q3 are respectivelyconnected to multiple ball terminals B2-1, B4-1, and B6-1 belonging tothe BGA terminals B1-1-Bn-m via the respective pads P2-1, P4-1, P6-1 ofthe IC chip 11A and the bumps associated with the pads. These collectorsare preferably connected with one another.

The multiple ball terminals B2-1, B4-1, and B6-1 to which the respectivecollectors of the transistor switches Q1-Q3 are connected are alsoconnected to one another outside the IC 10A. The multiple ball terminalsB2-1, B4-1, and B6-1 coupled together are connected to the node of thecoil Lo and the diode Do.

It should be understood that although three ball terminals are connectedto the coil Lo in the example shown, two ball terminals will besufficient in order to shunt the current Io. However, to ensurereduction of Joule heat due to the resistance Rb of a ball terminal(including contact resistance and wiring resistance) and to prevent theswitching circuit from being influenced by breaking of wires and/orloose contact of pads, more than two wires are preferably connected tothe coil Lo.

As the transistor switches Q1-Q3 are turned on, the current To flowingthrough the coil Lo increases with time. The current Io is shuntedevenly to the multiple ball terminals B2-1, B4-1, and B6-1, therebyproviding each of the transistor switches Q1-Q3 with current of aboutIo/3.

When the transistor switches Q1-Q3 are turned off, the energyaccumulated in the coil Lo will be liberated to the diode Do and thecapacitor Co, where the current is rectified and smoothed before it isoutput as the output voltage Vout. The output voltage Vout may becontrolled in the same manner as conventional, as described inconnection with FIG. 3.

This arrangement permits the shunted current to each of the parallellyconnected multiple ball terminals B2-1, B4-1, and B6-1 to be reduced toor below a permissible level, and causes the Joule heat due to thecontact resistance of the IC 10A with the substrate to be sufficientlyreduced. Accordingly, hazardous melting of the ball terminals of the BGAstructure can be avoided.

Since the resultant contact resistance of the multiple ball terminals isreduced to Rb/3, the power loss by the terminals and their surroundings,is reduced. In addition, the Joule heat is distributed over the multipleball terminals. Thus, the conversion efficiency of the power supply unitis improved accordingly.

It will be appreciated that the switch circuit is little influenced bybreaking of wires and/or loose contact of the pads if it happens, due tothe fact that the multiple ball terminals B2-1, B4-1, and B6-1 areparallelly connected and so are the switching transistors Q1-Q3.

Referring again to FIGS. 1 and 2, it is shown that each pair of nearestneighbors of the multiple ball terminals B2-1, B4-1, and B6-1 isprovided therebetween at least one interposing ball terminal B3-1 andB5-1 other than the multiple ball terminals. It should be understoodthat there can be more than one interposing ball terminal between eachpair of nearest neighbors of the multiple ball terminals B2-1, B4-1, andB6-1.

These interposing ball terminals are terminals through which flows no oran extremely small amount of current (e.g. Io/10) as compared with thecurrent (Io/3) flowing through the multiple ball terminals B2-1, B4-1,and B6-1.

By placing at least one such interposing terminal in between each pairof nearest neighbors of the multiple ball terminals in the manner asdescribed above, not only the resultant resistance of the multiple ballterminals is reduced but also the heat radiating area thereof isincreased and dispersed, thereby facilitating suppression of thetemperature rise in the respective multiple ball terminals.

All the multiple ball terminals B2-1, B4-1, and B6-1 are located at theoutermost peripheral terminal positions of the BGA configuration. Thus,external wiring leads connected to these terminals can be made thickerto reduce their electric resistances and enhance their heat-dissipativepower as compared with those connected to terminals located at innerterminal positions of the BGA structure.

It will be understood that, although the invention has been describedwith a particular reference to a BGA structure, the invention is notlimited to the example as described and shown above. For example, theinvention contemplates an IC having a pin gripped array (PGA) structurein which pluralities of pin-shaped terminals are arranged in a latticeconfiguration on one side of the IC.

The invention can be applied to a wide range of switching power supplyunits utilizing a switching circuit, including a step-up dc-dcconversion type power supply unit as shown in FIG. 1, a step-down dc-dcconversion type power supply unit and a step-down dc-ac conversion typepower supply unit. The invention can be also applied to motor driversutilizing a switch circuit.

1-31. (canceled)
 32. A semiconductor device comprising a plurality ofgrid alley terminals and incorporating a switch circuit composed of aplurality of transistor switches connected in parallel, wherein controlelectrodes of the plurality of transistor switches are connectedtogether, an output electrode of the switch circuit is connected to aplurality of terminals among the grid array terminals, and the pluralityof terminals are connected together inside the semiconductor device. 33.The semiconductor device according to claim 32, wherein the plurality oftransistor switches are bipolar transistors.
 34. The semiconductordevice according to claim 32, wherein the plurality of transistorswitches are MOSFETs.
 35. The semiconductor device according to claim32, wherein the plurality of terminals are arranged such that at leastone other terminal is located between every two of the plurality ofterminals.
 36. The semiconductor device according to claim 35, whereinthe other terminal is a terminal in which no current, or only anextremely small current compared with a current passing through theswitch circuit, passes.
 37. The semiconductor device according to claim35, wherein the plurality of terminals are all outermost peripheralterminals among the grid alley terminals.
 38. The semiconductor deviceaccording to claim 32, wherein the grid alley terminals are ball gridalley terminals.
 39. The semiconductor device according to claim 32,further comprising a drive circuit which turns the plurality oftransistor switches on and off simultaneously, wherein as the switchcircuits are turned on and off, an input voltage is converted into anoutput voltage, which is output.